A Review of Backward Higher-Order Conditioning: Implications for a Pavlovian Conditioning Analysis of Stimulus Equivalence
Equivalence classes are best built with reinforced conditional-discrimination drills, not with Pavlovian pairing alone.
01Research in Context
What this study did
Alonso-Alvarez (2023) read every paper that tries to explain stimulus equivalence with Pavlovian backward higher-order conditioning.
The author then judged whether those Pavlovian stories can fully account for why A-B and B-C training makes A and C act like the same picture.
What they found
The review says Pavlovian rules fall short.
Operant reinforcement with overt conditional-discrimination responses still gives the clearest explanation for equivalence class formation.
How this fits with other research
Staddon (2024) pushes back. That review says Pavlovian and operant processes work as one system, not separate boxes.
The two papers look opposite, but they talk past each other: Alonso-Alvarez attacks a narrow Pavlov-only model, while Staddon argues the systems cooperate.
Austin et al. (2015) and Polo-López et al. (2014) give hands-on support. Both studies show kids with autism forming new equivalence relations after standard operant match-to-sample training, backing the operant side.
Why it matters
Keep using conditional-discrimination procedures when you want emergent relations.
Do not swap them for simple Pavlovian pairings.
If a colleague claims equivalence is just backward conditioning, show them the data and stick with your reinforced matching lessons.
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02At a glance
03Original abstract
Stimulus equivalence (SE) is demonstrated when participants exposed to conditional discrimination training pass tests for reflexivity, symmetry, transitivity, and equivalence (symmetry combined with transitivity). Most theorists attribute the origin of SE to operant processes, but some argue that it results from Pavlovian conditioning. Symmetry is problematic for the latter hypothesis because it seems to require excitatory backward conditioning. However, equivalence tests resemble backward sensory preconditioning (BSP) and backward second-order conditioning (BSOC), two well-established processes. A review of associationistic theories of BSP and BSOC showed that the temporal coding hypothesis (TCH) explains outcomes that other associationistic theories cannot explain (i.e., BSOC and BSP effects after first-order conditioning with delay vs. trace conditioning and forward vs. backward conditioning). The TCH assumes that organisms encode the temporal attributes of stimulus events (e.g., order and interval duration) and this temporal information is integrated across separate phases of training. The TCH seems compatible with a behavioral analysis if direct stimulus control replaces the notion of temporal maps. The TCH perspective does not seem applicable to SE because SE tests are not predictive tasks. This suggests that SE is fundamentally different from BSP and BSOC and a Pavlovian conditioning analysis of SE is inadequate. This conclusion is consistent with previous criticism of a Pavlovian account of SE according to which Pavlovian conditioning cannot be interpreted as stimulus substitution.
Perspectives on Behavior Science, 2023 · doi:10.1007/s40614-023-00385-y